Infestation by head lice (Pediculus capitis) has become a worldwide problem and has been steadily increasing during the past three decades. Head lice are a very serious problem in Israel with at least 30% infestation, particularly of young school children.
There are a number of commercial insecticides such as allethrin, pyrethrum, malathion and carbaryl that are quite effective as licides but not very effective as ovicides to lice eggs. Carbaryl has been the most effective provided this insecticide is applied to the infected region for about twelve hours. Further there are a number of side effects which have been recorded for this carbamate and include nausea, vomiting, diarrhea, blurred vision, cyanosis, convulsions and coma.
According to the U.S. National Institute for Occupational Safety and Health (NIOSH), there are indications that Carbaryl (1-naphthyl-N-methylcarbamate), is carcinogenic in animals. It has now been found that the highly effective pyrethroids such as permethrin resmethrin and natural pyrethrins are becoming less effective to the house fly, horn fly and mosquitoes [Golenda & Forgash, J. Econ. Entomol., 78, 19 (1985); Schmidt et al., ibid, 78, 402 (1985); Scott & Georghiou, ibid, 78, 316 (1985)]. It is known that the pyrethroids are not stable in air and light and gradually lose their activity within a short time. Malathion has also been found to be less effective to a number of insects and is limited in its use to animals and man.
It has been disclosed by McFarlane & Henneberry [Comp. Biochem. Physiol., 24, 377 (1968)] that C.sub.12 fatty acids, among others, inhibit the growth of crickets. It has been found that C.sub.8 -C.sub.11 fatty acids, such as undecanoic acid, are effective insecticides to beetles, Calandra oryzae [Ikan, Shaaya and Grossman, Israel J. Entomology, XI, 81, 1976]. These fatty acids are also useful for protecting store products, such as wheat, as they are effective insecticides to certain beetles such as Callosobruchus chinensis and Calandra oryzae [Israel Patent No. 53570]. These fatty acids also act as effective larvicides to the housefly (Musca domestica) [Quraishi & Thorsteinson, J. Econ. Entomol., 58, 400 (1965)]; Tribolium confusum [House & Graham, Can. Entomol., 99, 994, (1967)] and mosquito larvae [Can. Entomol., 103, 1435 (1971)].
It has been disclosed that octanoic acid has ovicidal activity to the eggs of Aedes aegypti, [J. Econ. Entomol , 65(1), 177 (1972)].
Recently C.sub.2 to C.sub.8 carboxylic acids have been mentioned in U.S. Pat. No. 4,518,593 as active ingredients in insecticidal compositions for use in shampoos against lice and fleas. Only acetic acid was used in the examples and specifically claimed. Surprisingly this disclosure clearly states that upon replacing acetic acid by propionic acid or caprylic acid the results were substantially inferior to acetic acid.
U.S. Pat. No. 1,589,866 relates to the use of fatty acids as insecticides to destroy plant parasites and fungi. The patent does not mention licidal activity or application to any species of the Anaplura and in particular Pediculus capitis.
U.S. Pat. No. 2,396,012 relates to compositions used as insect repellents, these compositions containing active antimicrobial agents, one of the agents mentioned being n-capric acid. The patent does not mention any possible specific licidal and ovicidal activity of the agents mentioned therein.
U.S. Pat. No. 4,406,884 relates to antimicrobial compositions containing C.sub.5 -C.sub.12 fatty acids in the treatment of skin disorders. There is no mention in the patent of any possible licidal effect of the acids and none of the skin disorders mentioned therein relate to lice infestation.
An article by Robert E. Rakel in Conn's Current Therapy, 1984, pages 657-658, teaches the use of shampoos containing certain specific insecticides for the treatment of lice. The insecticides mentioned are known licidal agents, namely Lindane (gamma-benzene hexachloride), Crotamiton, Pyrethrins and Malathion. There is no mention in this reference of the use of any fatty acids as licidal shampoos.